“Structural characteristics of lignin are critical to enhance 3D printability of the materials."
Oak Ridge National Laboratory (ORNL) scientists have created a new composite material to be used for 3D printing that makes use of lignin - a biorefinery by-product. According to Tennessee-based ORNL, this feedstock could spur a profitable new use lignin.
The discovery was detailed in scientific journal Science Advances. Lignin is the material left over from the processing of biomass. It gives plants rigidity and also makes biomass resistant to being broken down into useful products.
“Finding new uses for lignin can improve the economics of the entire biorefining process,” said ORNL project lead Amit Naskar.
In a statement, ORNL (@ORNL) scientists said that they combined a melt-stable hardwood lignin with conventional plastic, a low-melting nylon, and carbon fibre to create a composite with “just the right characteristics for extrusion” and weld strength between layers during the printing process, as well as “excellent mechanical properties”.
The scientists said the process to form this composite was “tricky” because lignin “chars easily”. To solve this problem, researchers said that they combined lignin with nylon and found that “temperature stiffness increased while its melt viscosity decreased”.
According to the researchers, the lignin-nylon material had tensile strength similar to nylon alone and lower viscosity than conventional acrylonitrile-butadiene-styrene.
They found that the combination of lignin and nylon “appeared to have almost a lubrication or plasticising effect on the composite,” Naskar explained.
“Structural characteristics of lignin are critical to enhance 3D printability of the materials,” said ORNL’s Ngoc Nguyen who collaborated on the project.
Scientists were also able to mix in a higher percentage of lignin—40% to 50% by weight—a new achievement in the quest for a lignin-based printing material. ORNL scientists then added 4 to 16% carbon fibre into the mix. The new composite heats up more easily, flows faster for speedier printing, and results in a stronger product.
“ORNL’s world-class capabilities in materials characterisation and synthesis are essential to the challenge of transforming by-products like lignin into coproducts, generating potential new revenue streams for industry and creating novel renewable composites for advanced manufacturing,” said Moe Khaleel, associate laboratory director for Energy and Environmental Sciences.
The lignin-nylon composite is patent-pending and work is ongoing to refine the material and find other ways to process it. The ORNL research team also included Sietske Barnes, Christopher Bowland, Kelly Meek, Kenneth Littrell and Jong Keum. The research was funded by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy’s Bioenergy Technologies Office.